Astellas Agreements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended
	Oct. 21, 2022	Oct. 31, 2022	Mar. 31, 2021	Sep. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued				186,960,193			186,960,193	63,207,507
Probability of option exercise		50.00%
Decrease in revenue previously recognized					$ 3,100	$ 3,100
Revenues				$ 4,746			$ 11,847
Deferred revenue recorded within current liabilities				18,759			18,759	$ 33,557
Deferred revenue recorded within long-term liabilities				2,951			2,951
TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment			$ 5,500
Rett Research and Development Activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				2,400			9,500
Option Agreement for GAN
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				$ 2,300			2,300
Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment	$ 20,000
Transaction price		$ 36,100					36,059
Deferred revenue		$ 36,100
Astellas | Astellas Securities Purchase Agreement | Astellas Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued	7,266,342	7,266,342
Aggregate gross proceeds	$ 30,000
Fair value of shares transferred, Value		$ 13,950
Share price		$ 1.92
Transaction price		$ 16,100
Difference of market value paid		$ 30,000
Astellas | TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment							20,000
Transaction price							36,100
Astellas | TSHA-120 | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price							16,100
Astellas | Rett Research and Development Activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price							$ 28,257